Ice Core Records of Climate and Environmental Variability in the Tropical Andes of Peru: Past, Present and Future Registros en Núcleos de Hielo de la Variabilidad Climática y Ambiental en los Andes Tropicales del Perú: Pasado, Presente y Futuro Lonnie G. Thompson1,2, Ellen Mosley-Thompson1,3, Mary E. Davis1 and Stacy E. Porter1 1Byrd Polar and Climate Research Center, The Ohio State University, Columbus, Ohio 43210, USA 2School of Earth Science, The Ohio State University, Columbus, Ohio 43210, USA 3Department of Geography, The Ohio State University, Columbus, Ohio 43210, USA https://doi.org/10.36580/rgem.i3.25-40 Abstract Keywords: Peruvian glaciers, climate, El Niño, warming, In the Peruvian Andes mid-tropospheric warming, glacier retreat enhanced by recent strong El Niños, is destroying Resumen the climate signals preserved in the ice fields and accelerating glacier retreat. Nowhere is the loss En los Andes peruanos, el calentamiento de la of tropical glaciers better documented and more troposfera media, potenciado por el reciente fuerte important than in the Andes of Peru. The longest El Niño, está destruyendo las señales climáticas record of glacier retreat comes from a 44-year study preservadas en los campos de hielo y acelerando la conducted on the Quelccaya ice cap in southern retirada de los glaciares. En ninguna parte está mejor Andes, which substantiates the loss of a very important documentada la pérdida de los glaciares tropicales climate archive as well as the accelerating loss of a y es más importante que en los Andes del Perú. El water resource that feeds the Amazon River and Lake registro más largo de retirada de glaciares proviene Titicaca. In the Cordillera Blanca the glaciers below de un estudio de 44 años realizado en el casquete de 5400 masl are undergoing both seasonal melting hielo Quelccaya en el sur de los Andes, que prueba and the movement of melt water through the porous la pérdida de un archivo climático muy importante upper layers. Because of its high elevation Nevado y la pérdida acelerada de un recurso hídrico que Huascarán is one of a few tropical sites where a alimenta el río Amazonas y el lago Titicaca. En la largely unaltered climate history, which extends back Cordillera Blanca, los glaciares por debajo de los to the Last Glacial Stage, is still being preserved. 5400 msnm sufren tanto un deshielo estacional However all the Cordillera Blanca glaciers are como el movimiento del agua de deshielo a través documented by INAIGEM (in press) to be retreating. de las capas superiores porosas. Debido a su gran Given the current rates of warming throughout the altitud, el nevado Huascarán es uno de los pocos tropical Andes, it is only a matter of time before sitios tropicales donde aún se conserva una historia climate records from Huascarán ice will also be climática prácticamente inalterada, que se extiende lost. The glacier retreat throughout the Peruvian hasta la última etapa glacial. Sin embargo, todos los Andes is contributing to emerging water resource glaciares de Cordillera Blanca documentados por crises and environmental hazards for both urban and INAIGEM (en prensa) estar en retroceso. Dadas rural populations. Although currently the dry season las tasas actuales de calentamiento en los Andes discharge is increasing, it will not be sustained in the tropicales, solo es cuestión de tiempo para que los longer term. Most of Peru’s population lives in the registros climáticos del hielo del Huascarán también west coast desert, which relies on glacier fed streams se pierdan. El retroceso de los glaciares a lo largo de for agriculture and livelihoods. Melting glaciers los Andes peruanos está contribuyendo a las crisis also exacerbate geohazards in this earthquake-prone emergentes de los recursos hídricos y los peligros region by forming ice and moraine-dammed glacial ambientales tanto para las poblaciones urbanas lakes, which can result in lake outbursts and flooding como rurales. Aunque actualmente la descarga de la and debris flows. Understanding the impact of this estación seca está aumentando, no se mantendrá así a acceleration of glacier loss on future water resources largo plazo. La mayoría de la población del Perú vive requires information about past changes in high en el desierto de la costa oeste, que depende de los elevation glacier mass balance. ríos alimentados por los glaciares para la agricultura y los medios de subsistencia. El derretimiento de los glaciares también agrava los peligros geológicos en

Revista de Glaciares y Ecosistemas de Montaña 3 (2017): 25-40 25 L. Thompson, E. Mosley-Thompson, M. Davis and S. Porter

esta región propensa a terremotos, formando lagunas area and volume measurements, will undoubtedly glaciares con represas de hielo o morrenas, lo que have meaningful social and economic implications puede dar como resultado estallidos de lagunas e for understanding climate change and the potential inundaciones y flujos de escombros. Comprender el impacts on water resources. It is of paramount impacto de esta aceleración de la pérdida de glaciares importance to attain a better grasp of the climatic en los recursos hídricos futuros requiere información factors that control the recent low-latitude glacier sobre los cambios del pasado en el balance de masas responses. Moreover, the continued loss of glaciers de los glaciares de alta elevación. and ice caps will increasingly compromise and eventually obliterate most of the non-polar, ice core- Palabras clave: Glaciares peruanos, clima, El Niño, derived climate histories. This is a particular concern calentamiento, retiro de glaciares in the Peruvian Andes, where mid-tropospheric warming, enhanced by recent strong El Niños, is now Introduction destroying the climate signals preserved in the ice Scientific evidence of variations in the atmosphere- fields and accelerating glacier retreat. ocean-climate system verifies that Earth’s globally averaged surface temperature is increasing, and a recent international assessment (Vaughan et al., 2013) indicates that human activities are contributing to these observed changes in the Earth system. Low- latitude paleoclimate histories are critical for the acquisition of a global array of ice cores that provide high-resolution climatic and environmental histories essential for understanding the complex interactions within Earth’s coupled climate system. Improved predictive capability requires better quantification of the system’s physical and chemical linkages along with the complex feedbacks that may dampen or accelerate the initial forcings. Ice core records from Africa, Alaska, Alps, Antarctica, Bolivia, China, Greenland, Peru, Papua (Indonesia) and Russia have made it possible to study processes linking the Polar Regions to the lower latitudes where human activities are most concentrated. The diverse and frequently detailed information obtained from ice cores contributes prominently to Earth’s paleoclimate record, the ultimate yardstick against which the Figure 1. Map of Peru and northwest Bolivia showing significance of present and projected anthropogenic locations of high elevation ice fields mentioned in text from which ice cores have been recovered. Inset: Google Earth effects will be assessed. image of Cordillera Blanca (corresponding to black box in map) showing locations of the mountains from which shallow It is imperative to understand Earth’s climate and deep ice cores have been recovered. HS is emphasized by regime, both past and present. Fifty percent of the yellow triangle. Earth’s surface lies between 30oN and 30oS, where Nevado Huascarán (HS, 9.1oS; 77.6oW; 6757 70% of the world’s inhabitants live and conduct their masl at the highest point, the South Peak summit; activities. Temperate and tropical ice cores offer INAIGEM, 2017) in the Cordillera Blanca of central long-term perspectives of variability in precipitation, Peru is located ~200 km from the western edge of temperature, aridity and atmospheric circulation that the Amazon Basin (Figure 1). Two ice cores that are unavailable from other proxy sources. Ice core were drilled in the col by the Byrd Polar and Climate data allow detailed reconstruction of both climate Research Center at The Ohio State University (OSU- variability and climate forcings (e.g., volcanic and BPCRC) in 1993 provided a paleoclimatic history solar activity) as well as the timing of the most recent extending well into the Last Glacial Stage (LGS), glaciation at different latitudes and altitudes. The which includes evidence of the Younger Dryas cool results from these analyses, as well as from glacier phase in the Tropics (Thompson et al., 1995).

26 Revista de Glaciares y Ecosistemas de Montaña 3 (2017): 25-40 Ice Core Records of Climate and Environmental Variability in the Tropical Andes of Peru: Past, Present and Future

Figure 2. Top 100 years of HS record from the 1993 Core 2 showing the seasonal variations in δ18O

and concentrations of dust and nitrate (NO3-). El Niño events (Quinn, 1983) are noted by white (M=moderate, M+=moderate plus) and black (S=strong, S+= strong plus, VS=very strong) boxes (from Thompson, 2000).

Results of Past Research on Huascarán Ice resolution was limited to the top 270 years. The Cores timescale was originally based on a combination of 18 HS receives abundant snow accumulation (~2 to 3 ice flow modeling and δ Oice matching with a North meters/year) and contains distinct seasonal variability Atlantic marine core (Bard et al., 1987). A strong in δ18O and concentrations of dust and certain ions warming has dominated the last two centuries at the (Figure 2). The majority of the precipitation in the HS site. Peruvian Andes falls during the austral summer (December to February, DJF) (Garreaud et al., 2003; Since the initial publication the Holocene timescale Mantas et al., 2015) in association with the South has been fine-tuned using 18δ O measurements of air American summer monsoon (SASM). Although from bubbles in the ice (Thompson, 2000; Davis 70% of Earth’s tropical glaciers are located in Peru, and Thompson, 2006). A middle-Holocene dust only HS situated just above the Amazon Basin is event (MHDE), originally dated at ~2000 yrs BP, documented to contain a ~20,000 history of tropical was determined to have occurred ~4500 yrs BP, climate variability. LGS conditions at high elevations which is contemporaneous with a mid-Holocene in the Tropics appear to have been as much as 8 to drought documented in many paleoclimate records 12 °C cooler than today, the atmosphere contained throughout the world (Figure 3). The refinement of about 200 times as much dust (Figure 3), and the the Holocene timescale also allowed us to determine Amazon Basin forest cover may have been much that the last time that the HS isotope record was as less extensive (Thompson et al., 1995) (Figure 4). enriched as it is today was ~6 thousand years ago Differences observed in both the δ18O (8‰) and the (ka), when wetland plants were exposed in the last deuterium excess (4.5‰) from the Late Glacial Stage decade along the margin of the retreating Quelccaya to the Holocene are comparable with those observed ice cap (Thompson et al., 2013). This was determined in other low latitude cores from Bolivia and Tibet by radiocarbon dating of the plants that had grown by as well as those from polar ice core records. These the margin of the ice cap and then were buried as the data imply that the tropical Atlantic was possibly 5 margin advanced during the middle to late Holocene to 6 °C cooler during the LGS, that the Holocene cooling (Figure 3). This supports a temperature- climate was warmest from 8400 to 5200 years before linked interpretation of δ18O in the HS climate record, present (yrs BP) then cooled gradually, culminating at least on centennial to millennial timescales. in the Little Ice Age (200 to 500 CE). Because of the rapid thinning in the HS cores below 120 m, annual

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Figure 3. The ~19 thousand year record (100-year averages) of climate and environmental variations from the 1993 HS Core 2. A plant found by the margin of the retreating Quelccaya ice cap in southern Peru is 14C dated at ~6 ka and shows the climate conditions on HS at the time the margin of Quelccaya was growing (Thompson et al., 2013). The Mid-Holocene Dust Event (MHDE) is shown by the dust concentration spike ~4.5 ka.

Figure 4. Illustration of changes in major vegetation types at the Last Glacial Maximum compared to those today as inferred by Clapperton (1993).

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Atmospheric and Oceanic Influences on Ice the Amazon (Grootes et al., 1989), tropical Pacific sea Fields of the Cordillera Blanca surface temperatures (Bradley et al., 2003; Thompson The intensity of the SASM is influenced by et al., 2011, 2013), ENSO-related atmospheric convection enhanced by a deep low-pressure system circulation (Henderson et al., 1999; Bradley et al., that forms in the summer over the Chaco region 2003; Vuille et al., 2000, 2003) and SASM dynamics (eastern Bolivia, western Paraguay and northern (Hurley et al., 2015). Recent studies of tropical Argentina). The latent heat from the convection precipitation, however, conclude that convection- contributes to the formation of the Bolivian High, a associated condensation temperature exerts a major persistent upper level high pressure system over the influence (Scholl et al., 2009; Cai and Tian, 2016; Bolivian Altiplano and southeastern Amazon Basin Permana et al., 2016). (Lenters and Cook, 1997). Anticyclonic circulation associated with the Bolivian High results in upper Henderson et al. (1999) analyzed the top 68 and mid-level easterly to northerly transport of moist years of the 1993 HS δ18O record and found that air to the Andes which strengthens deep convection spatial distributions of temperature anomalies in the over this region (Garreaud et al., 2003, 2009). The western tropical Atlantic influence the 500 mb zonal El Niño-Southern Oscillation (ENSO) has a strong circulation, which affects the isotopic fractionation influence on moisture transport from the Amazon of moisture over the Amazon Basin. During El Niño, to the central Andes, partly through variations in warm and dry conditions occur over northeastern westerly airflow over the central Andes which affects Brazil due to a northward shift of moisture low and mid-level easterly flow from the northern convergence over the Atlantic, which often results in Amazon Basin during the austral summer (Vuille et 18O enrichment in Cordillera Blanca snow. al., 2000; Garreaud and Aceituno, 2001). Strong El Niños are responsible for anomalous warming of up Using δ18O from pit and shallow core samples on HS to 4 oC in the middle troposphere in the Tropics, which and Quelccaya in the Cordillera Vilcanota, Thompson has significant impacts on freezing level heights (Diaz et al. (2017) demonstrated the influence of tropical et al., 2014). atmospheric and eastern Pacific oceanic processes on the stable isotopic values of snow deposited in the Snow layers deposited on tropical Andean Peruvian Andes. Isotopic fractionation of moisture glaciers during austral summer are isotopically for both ice fields is linked to eastern equatorial depleted relative to winter layers (June to August, Pacific sea surface and high cloud top temperatures or JJA) (Thompson, 1980; Hurley et al., 2015). (SSTs and CTTs, respectively) and tropical western In their analysis of automatic weather station and hemisphere mid-tropospheric temperatures (Figure snowpit data on the summit of the Quelccaya ice 5). For HS in particular, austral summer snow that cap in southern Peru, Hurley et al. (2015) found is characterized by overall high, or 18O enriched that sublimation and water vapor diffusion through (low, or 18O depleted) δ18O values is significantly the surface snow promote 18O enrichment during correlated with high (low) SSTs in the NIÑO3.4 the dry season when little fresh snow is deposited. region and high (low) 500 mb temperatures over the In addition, snowfall amounts on seasonal to decadal tropical eastern Pacific and northern South America. timescales can be influenced by tropical atmospheric CTTs in the tropical Pacific over the NINO3.4 region and oceanic processes (Vuille et al., 2000; Garreaud are negatively correlated with δ18O, indicating deep et al., 2003; Thompson et al., 2013; Hurley et al., convection during these warm austral summers. All 2015). However, the interpretation of stable isotopic these relationships are symptomatic of ENSO events. ratios of oxygen (δ18O) and hydrogen (δD) in tropical However, the fact that the relationship between δ18O precipitation has been controversial, especially with on HS and the tropical Pacific climate variables regard to the influence of air temperature versus remains stable during non-ENSO events suggests precipitation amount. Early studies (Dansgaard, that HS may capture tropical variability that is not 1964; Rozanski et al., 1993) indicate that for tropical necessarily affiliated with individual ENSO events rainfall, precipitation amount is the more important (e.g., underlying trends, multi-decadal variability). influence on stable isotope chemistry. However, other This is contrary to Quelccaya, where strong ENSO atmospheric and oceanic processes undoubtedly events have major impacts on snow isotope chemistry affect isotopic ratios to varying degrees. In the (Thompson et al., 2017). However, impacts of El Niño tropical Andes these include air mass stability over on HS may have been differentially stronger before

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Figure 5. Pearson 2-tailed correlation (R) fields between HS thermal year 18δ O (1973/74 to 1992/93, 2012/13 to 2015/16) and (a) DJF SSTs (Huang et al., 2015; Liu et al., 2015), (b) DJF 500mb-T (Kalnay et al., 1996), and (c) DJF CTTs (Kalnay et al., 1996). Red shading indicates positive R, blue shading indicates negative R, and black contours denote R values with significance levels (p) < 0.05. Adapted from Thompson et al. (2017). the middle 1970s, since the correlation between provide evidence that it has been retreating along its equatorial eastern Pacific SSTs in the NIÑO3.4 margins (Brecher and Thompson, 1993; Thompson et region and mass balance of Cordillera Blanca glaciers al., 1982, 2006, 2013; Albert et al., 2014; Hanshaw changed from significant to insignificant after this and Bookhagen, 2014). This long-range retreat time, perhaps because of multi-decadal Pacific Ocean is overprinted by variations in temperature and temperature reorganization (Vuille et al., 2008). precipitation during El Niños, the most recent of These relationships add to earlier research indicating which (2015/16) was associated with a dramatically that the isotope chemistry in Andean precipitation is higher rate of ice wastage compared with that of the strongly influenced not only from the east (Grootes et previous 15 years (Thompson et al., 2017). In the al., 1989; Henderson et al., 1999; Hurley et al., 2015), Cordillera Blanca, the relationship between El Niño but also by perturbations in the Walker circulation and mass balance is generally consistent, with many during ENSO events that in turn are affected by investigators noting negative correlations between oceanic processes (Vuille et al., 2003; Vuille and tropical Pacific SSTs and glacier mass balance (Kaser Werner, 2005; Thompson et al., 2013). et al., 2003; Vuille et al., 2008; Maussion et al., 2015). This suggests that warming from future El Niños may The effects of strong El Niños are seen not only accelerate the ongoing mass loss trends on Peruvian in the chemistry of the climate record from Andean glaciers. glaciers but also in the ice coverage. Glaciological observations of the Quelccaya ice cap since the 1970s

30 Revista de Glaciares y Ecosistemas de Montaña 3 (2017): 25-40 Ice Core Records of Climate and Environmental Variability in the Tropical Andes of Peru: Past, Present and Future

Glacier Status in the Andes by 15%, from ~721 km2 to 600±61 km2 (Silverio Evidence is mounting that the rate of tropospheric and Jaquet, 2005). Schauwecker et al. (2014) found warming is increasing with elevation due to factors that although the temperature rise in the Cordillera such as latent heat release, atmospheric aerosol Blanca has slowed while precipitation has increased loading, and feedbacks involving albedo, water from 1983 to 2012, the rate of glacier retreat has vapor, and radiation fluxes (Pepin et al., 2015). The continued unabated, perhaps due to an imbalance current warming has had detrimental effects on the between the meteorological forcing and the slower mass balances of many tropical ice caps and glaciers. glacier response before 1980. However, they suggest Many glaciers in the tropical Andes are diminishing that small and low-elevation glaciers may disappear at faster rates than at any time since the middle of in the near future. Glacier area on Nevado Pastoruri/ the Little Ice Age (Thompson et al., 1993, 2013; Caullaraju (Figure 1, insert) has decreased 58% Francou et al., 2003) and slightly faster than glacier between 1975 and 2010 (Durán-Alarcón et al., 2015), retreat on a global scale (Rabatel et al., 2013). The and glacier area in the Yanamarey catchment has most rapid rate of retreat has occurred in the last 50 decreased to one third of its 1975 extent while mean years (Rabatel et al., 2013), and many small, low- annual temperature has increased by 0.21 oC/decade elevation glaciers in the tropical Andes are projected (López-Moreno et al., 2017). to disappear within a few decades (Vuille et al., 2008; Rabatel et al., 2013; Schauwecker et al., 2014). The isotopic data from HS and other glaciers in During the 20th century, temperature has shown a the Cordillera Blanca demonstrate how the recent more consistent upward trend while precipitation warming over the tropical Andes has affected the has shown little consistent trend, thus precipitation is preservation of the climate records in the upper not considered to be the primary factor driving the layers of these ice fields (Figure 6). Over 25 years ice retreat (Rabatel et al., 2013). The national glacier ago a number of ice fields (< 6000 masl) considered inventories in Peru have cataloged a 40% total loss to be potential drill sites in the Cordillera Blanca of glacier-covered areas between 1970 and 2003- were sampled and found to already be experiencing 2010 (UGRH, 2014). Between 1970 and 1996 the smoothing of their seasonal δ18O variations. On the glacier coverage in the Cordillera Blanca diminished

Figure 6. Ice core δ18O records from Cordillera Blanca ice fields (locations in Figure 1) arranged by increasing elevation. The drilling year of each ice core is indicated above its respective profile (modified from Davis et al., 1995, Figure 6).

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Figure 7. (a) δ18O profiles from selected Quelccaya summit cores drilled over the last four decades. (b) 18δ O profiles from the tops of the HS 1991 shallow core, the HS 1993 deep core, and the entire HS 2016 shallow core. Adapted from Thompson et al. (2017).

col of HS the firn and ice have retained the seasonal increasing 18O depletion throughout the Holocene (as isotopic variations both at the surface and at depth does Illimani, not shown), while the Sajama isotopic (Figure 6) due to the higher elevation (6050 masl). trend is more constant. All the Andes cores contain As the 0 oC isotherm is approaching the summit of a warm period ~14 to 15 ka corresponding to the the Quelccaya ice cap (5670 masl) the distinctive Allerød warming in the GISP2 record, followed by a seasonal δ18O oscillations in the fresh snow deposited climatic reversal that is concomitant with the Younger within each thermal year are attenuated at depth Dryas in Greenland. The HS record extends to the end (Figure 7) due to melting and percolation through of the last glacial cycle, while Sajama extends further the firn (Thompson et al., 2017). With continued into the LGS. Isotopic changes from the Last Glacial warming the HS climate record will likely become Maximum (LGM) to the Holocene are similar (5.1 similarly compromised in the future. to 6.5‰) for all the cores shown in Figure 8, from Antarctica through the tropical Andes to Greenland. Ice Core-derived Climate Records from The broad similarities between the Cordillera Blanca the Andes and Existing Information from and Bolivian Altiplano ice core δ18O records provide Huascarán evidence that the Amazon Basin is the dominant source of moisture for the tropical Andes. However, Ice core-derived climate records from the Andes moisture/aridity balances in these two areas exhibit of Peru and Bolivia span several timescales, from opposite trends. During the LGS the climate at 18oS relatively short (e.g., Quelccaya, 1800 years) to was cool and wet and was marked by local lake several millennia (HS, Coropuna, Sajama, Illimani). expansion (Thompson et al., 1998), while climate in The Quelccaya ice cap appears to be melting at its the Cordillera Blanca was cool and dry (Thompson et base (Thompson et al., 1985, 2013), thus removing al., 1995). This is suggested to result from a reduction time from the bottom. The HS record extends ~19 in Hadley cell intensity due to weakening of the ka (Thompson et al., 1995), Coropuna (15.5oS; tropical meridional temperature gradient during the 72.7oW; 6410 masl) covers ~16 ka (Buffen, 2008), LGS (Rind et al., 1998). Sajama (18.1oS; 68.9oW; 6542 masl) extends back ~25 ka (Thompson et al., 1998) and Illimani (16.6oS; The Holocene climate on HS is dominated by 67.75oW; 6350 masl) covers ~18 ka (Ramirez et al., gradual 18O depletion from ~9 ka to the Little Ice Age 2003). Note that these longer records were recovered (Figure 3) (Thompson et al. 1995; Thompson 2000). from above 6000 masl. HS and Coropuna δ18O show The most dramatic event during the Holocene is a

32 Revista de Glaciares y Ecosistemas de Montaña 3 (2017): 25-40 Ice Core Records of Climate and Environmental Variability in the Tropical Andes of Peru: Past, Present and Future

Figure 8. δ18O records from (A) HS at 9oS, (B) Coropuna in southern Peru at 15.5oS, and (C) Sajama on the Bolivian Altiplano at 18oS compared with polar records from (D) GISP2, Greenland, and (E, F) two records from Antarctica over the most recent 25 ka showing regional and hemispheric similarities and differences. large dust peak, the MHDE, which occurs at ~4.5 ka, Discussion and has been linked to a global-scale mid-Holocene arid period. Evidence for this has been found in many Tropospheric warming over the highest elevations locations at middle and low latitudes, including lake of the tropical Andes has been well documented in levels in northern Africa (Gasse, 1977, 2000; Gillespie recent decades (Vuille et al., 2015). Model results of et al., 1983; Servant and Servant-Vildary, 1980), the elevation dependent warming show that temperature Sea of Oman (Cullen et al., 2000), and the Indus delta increases will be maximized in the high Andes (Bradley (Staubwasser et al., 2003), the largest Kilimanjaro et al., 2006). A warming trend of ~0.10 oC/decade has ice field (Thompson et al., 2002), and northwest been observed in the central Andes over the last half India (Dixit et al., 2014). This event may have been century (Bradley et al, 2009), and future warming is associated with a protracted African/Asian/Indian projected to increase with altitude, potentially by 4 oC monsoon weakening which may have been associated by the end of the 21st century (Bradley et al., 2006; with a shift toward stronger and/or more frequent Urrutia and Vuille, 2009), with much of the warming ENSO events (Conroy et al., 2008). The MHDE occurring in the winter. There is extensive evidence appears as an abrupt 15-fold increase in submicron that this warming has been responsible for the mineral dust thought to have originated in the Bodélé dramatic retreat of many Peruvian glaciers, including region of North Africa and to have been transported the Quelccaya ice cap, along with the eradication by trade winds across the Atlantic and incorporated of their recent climate signals (Davis et al., 1995; in the moisture that was advected over the Amazon Thompson et al., 2006, 2013) (Figures 6 and 7). Two (Davis and Thompson, 2006). The presence in HS ice decades ago a number of ice fields (< 6000 masl) in the of unusually large dust particles (>40 μm diameter) Cordillera Blanca investigated as potential drill sites of similar mineralogy to the mountain indicates that were sampled and found be undergoing smoothing the aridity occurred in the Cordillera Blanca and of their seasonal δ18O variations (Davis et al., 1995, that more native rock was exposed as the ice cover see Figure 6). There is evidence that the melting and receded upslope from the col. percolation through the firn have been exacerbated in

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southern Peru by the effects of major El Niños, and in the Cordillera Blanca. The changes in the dust the most recent event (2015/16) has had particularly composition and concentrations can reflect changes in devastating effects on Quelccaya (Thompson et al., potential source areas and/or atmospheric circulation 2017). Evidence indicates that this most recent event at decadal, centennial, millennial, and glacial- has, at least temporarily, accelerated the rate of retreat interglacial timescales. HS lies under the influence of Quelccaya and enhanced the obliteration of the of easterly winds and a change in the sources of the climate record stored in the ice. above parameters in Amazonia, and possibly in North Africa, may be reflected in variations in the elemental While the oxygen isotopic record from the firn composition of aerosols entrained in the atmosphere core recovered from the col of HS in 2016 at 6050 and ultimately deposited on HS. For instance, the meters still preserves a largely unaltered seasonal Sahara was subjected to large environmental changes depositional signal it is only a matter of time during the mid-Holocene, including a major transition before this higher elevation record will be similarly from a green wet phase (African Humid Period) to dry compromised by the ongoing warming. In fact, ice desert conditions (Kröpelin et al., 2008). Amazonia area has already been reduced on HS and its neighbor might have experienced large environmental changes Nevado Chopicalqui by ~28% (from 65.6 km2 to 46.9 from rainforest to savanna-type vegetation and km2) between 1962 and 2016 (INAIGEM, in press). savanna forest from 22 to 13 ka. Figure 4 illustrates It is possible that the warming trend of the regional the vegetation and surface cover inferred for both climate is near or at a threshold beyond which modern and glacial stage conditions (Clapperton, additional warming from very strong El Niños like 1993). The Amazon forest may have split into a major the 2015/16 event, along with elevated freezing levels western Amazon and several other medium size and feedbacks such as reduced snow cover, will forests (van der Hammen and Absy, 1994). Others augment the ice loss on even the highest-elevation advance a scenario of long-term continuous forest Peruvian glaciers in the coming decades. occupation based on available palynological data from the Amazon Basin (Colinvaux and De Oliviera, Valuable tropical ice archives are rapidly 2000). The initial interpretation of the dust and nitrate disappearing so new methods of investigation are data from the 1993 HS core (Thompson et al., 1995; needed to extract and analyze the ice, both in the field Urrego et al., 2016) was consistent with drier, dustier and in the lab, with the maximum achievable temporal conditions in Amazonia during the LGS. resolution. Recovery and research should focus on ice cores from glaciers at risk of disappearing, using Conclusions new and fast methods of glaciological investigation to retrieve the cores quickly and to understand Ice can be considered to be Nature’s best climatic and environmental processes that might help thermometer, perhaps the most sensitive and guide mitigation and adaption approaches to climate unambiguous indicator of climate change (Pollack, change. Many key areas containing these icy archives 2009), and glaciers serve both as recorders and are experiencing geopolitical as well as climatic indicators of climate change. Ice cores recovered risks, but the competition for water in Peru is already from Peruvian glaciers contain climate histories growing and promises to worsen (see “A flood of that can be reconstructed from stable isotopes and problems, Peru’s glaciers have made it a laboratory aerosols, and they also hold the potential of a history for adapting to climate change. It’s not going well.” - of biological parameters (microbial populations, Miroff, 2017). pollen and even methane concentrations) at the highest elevation sites. The recent warming in the Data from the HS ice cores address three Tropics is observed not only in ice core chemistry, important research areas. The first involves filling the but in the retreat of the ice fields. Glaciers and ice information gap on how the climate and environment caps in the tropical Andes of Peru serve as first have changed over the past 24 years. The second is to responders to climate change as they expand when it provide high elevation mass balance data. Estimates is colder and/or wetter and retreat when it is warmer of snowfall totals in the accumulation zone of Andean and/or dryer much faster than large polar ice sheets. glaciers have large uncertainties (Vuille et al., in press) Numerous high altitude glaciers throughout the and the HS ice cores will provide important point- world are monitored by ground observations, aerial estimates of mass balance at the highest elevations photography, and satellite-borne sensors. From

34 Revista de Glaciares y Ecosistemas de Montaña 3 (2017): 25-40 Ice Core Records of Climate and Environmental Variability in the Tropical Andes of Peru: Past, Present and Future all these analyses there is a consensus that almost by policymakers, governmental agencies, and public without exception these ice fields are retreating at an resource administrators to help guide mitigation and accelerating rate (Coudrain et al., 2005; Thompson et adaptation strategies. al., 2006, 2011, 2013). Nowhere is the loss of tropical glaciers better documented and more important than References in the Andes of Peru. The longest documented record of tropical glacier retreat comes from a 44-year study Albert, T., Klein, A., Kincaid, J. L., Huggel, C., Racoviteanu, conducted on the Quelccaya ice cap (the largest of A. E., Arnaud, Y.,… Ceballos, J. L. (2014). Remote the tropical ice caps) in the southern Andes of Peru. sensing of rapidly diminishing tropical glaciers in Both ice core archives, as well as the detailed retreat the northern Andes. In Kargel, J. S., Leonard, G. of the Quelccaya’s largest outlet glacier (Qori Kalis), J., Bishop, M. P., Kääb, A. and Raup, B. H. (Eds.). document the loss of a very important climate archive Global Land Ice Measurements from Space, 609- as well as the accelerating loss of a water resource that 638. Berlin Heidelberg, Springer. feeds not only the Amazon River to the east but also Lake Titicaca to the south. In the Cordillera Blanca Bard, E., Arnold, M., Maurice, P., Duprat, J., Moyes, all the shallow ice cores from elevations below 5400 J. and Duplessy, J.-C. (1987). Retreat velocity masl document the alteration of the ice core record of the North Atlantic polar front during the last due to both seasonal melting and the movement of deglaciation determined by 14C accelerator mass melt water through the porous upper firn layers. spectrometry. Nature, 328, 791-794. https://doi. Because of its high elevation, only Huascarán appears org/10.1038/328791a0 to still preserve a largely unaltered ice core record. As in southern Peru, the Cordillera Blanca glaciers, Bradley, R. S., Vuille, M., Hardy, D. and Thompson, L. including Huascarán, are documented by INAIGEM G. (2003). Low latitude ice cores record Pacific sea (in press) to be retreating. Given the current rates of surface temperatures. Geophysical Research Letters, warming throughout the tropical Andes, it is only 30(4), 1174. https://doi.org10.1029/2002GL016546 a matter of time before ice core-derived climate records from Huascarán will also be compromised Bradley, R. S., Vuille, M., Diaz, H. F. and Vergara, W. and permanently lost. (2006). Threats to water supplies in the tropical Andes. Science, 312, 1755-1756. https://doi. Peru’s population is particularly vulnerable to org/10.1126/science.1128087 climate change. The current glacier retreat throughout the Peruvian Andes is contributing to emerging water Bradley, R. S., Keimig, F. T., Diaz, H. F. and Hardy, resource crises and environmental hazards for both D. R. (2009). Recent changes in freezing level urban and rural populations. Currently, this retreat is heights in the Tropics with implications for creating an enhanced dry season discharge that will the deglacierization of high mountain regions. not be sustained in the longer term. Most of Peru’s Geophysical Research Letters, 36, L17701. https:// population lives in the west coast desert, which relies doi.org/10.1029/2009GL037712 on glacier streams for agriculture, hydroelectricity, municipal water supplies, ecosystems, tourism Brecher, H. H. and Thompson, L. G. (1993). Measurement and recreation. Retreating glaciers also exacerbate of the retreat of Qori Kalis glacier in the tropical geohazards by forming ice and moraine-dammed Andes of Peru by terrestrial photogrammetry. glacial lakes, which can result in lake outbursts that Photogrammetric Engineering & Remote Sensing, often cause flooding and debris flows. These outbursts 59, 1017-1022. are even more likely in this earthquake prone region. Understanding the impact of this acceleration of Buffen, A. (2008). Abrupt Holocene climate change: glacier loss on future water resources requires Evidence from a new suite of ice cores from information about past changes in high elevation Nevado Coropuna, southwestern Peru and recently glacier mass balance. This information is sparse, exposed vegetation from the Quelccaya ice cap, with the exception of a few point-estimates based southeastern Peru. Masters thesis, The Ohio State on ice core studies such as those from the Cordillera University, 128 pp. Blanca, and especially on its highest ice field on Nevado Huascarán. Such data are urgently needed

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